Our washing mashine drain has a mildew like odor coming from it. I've poured some draino down it and wrapped it in duct tape for now. But is there some sort of premade seal or something for it? It looks like it'* keyed for a collar or something. But we just have this hose that sticks down in the hole about a foot. A quick look at Lowes.com didn't reveal anything like that.
I have never seen a seal for them, just the pipe sticking out and the drain hose dropped into it, similar to what you have, except usually I have seen the PVC pipe stick out of the "box" about three inches or so.
I would just try the bleach thing, sealing it with duct tape might not allow it to drain properly.